The instant invention relates to the soft start of all high-performance drive motors used as asynchronous motors for a rotor spinning machine. Asynchronous motors are used for the drive in rotor spinning machines. The installed electrical capacity of the drive is relatively high by comparison with machines for other spinning processes because the inertia masses are relatively high for each individual drive motor.
High-performance asynchronous motors are used on rotor spinning machines to drive the operating elements, particularly the rotors and opener rollers. The operating element rotors and opener rollers are driven by a separate asynchronous motor for each machine side in this instance.
The motor for main suction is also a high-performance asynchronous motor. These high-performance asynchronous motors produce a very large portion of the overall installed electrical capacity of the rotor spinning machine. The utilization of asynchronous motors has prevailed on rotor spinning machines because they require little maintenance, and are inexpensive and economical. When starting under load, these asynchronous motors produce high torque peaks which exceed the nominal torque considerably. This behavior in operation results in high mechanical stress on the drive shaft and coupling. Force transmission elements such as belts or operating elements such as rotors and opener rollers are thus subjected to great mechanical stress.
The high starting current produced as high-performance asynchronous motors are started is also disadvantageous. It causes the windings of the motor to heat up so that the electric strength is burdened. The high peak loads as the rotor spinning machine is started also burden the appertaining electrical supply network.
For these reasons asynchronous motors which were oversized because of the required acceleration of the inertia masses of the spinning machine or which are equipped with a starting aid were used. Known starting aids are the Y/delta connections, starting transformers, sliding couplings or electronic soft-start control apparatuses. Electronic soft-start control apparatuses have prevailed and are normally used when the driving power of an asynchronous motor is more than 15 kW. This characterizes a high-performance asynchronous motor. The control principle of a soft-start control apparatus is the phase control of the semiconductors. In known rotor spinning machines, a separate starting control is used for each asynchronous motor used to drive the rotors, the opener rollers, and the main suction. This represents high costs for this starting aid.